In an unusual twist of the climate change saga, polar bears and grizzly bears are increasingly interbreeding and scientists are taking note. Since 2006, several confirmed and unconfirmed sightings of “pizzly bears” have been reported as climate change alters the habitat and habits of the two species. As the Arctic continues to warm at a disproportionately rapid rate, continued hybridization of bears and other mammals may be inevitable.
“We’ve known for decades that, in captivity, grizzly bears and polar bears will hybridize and in fact produce fertile offspring,” says Dr. Brendan Kelly, chief scientist and director of conservation research at the Monterey Bay Aquarium and long-time researcher of Alaskan ecology. This compatibility is not unexpected due to the bears’ shared ancestry. “It’s important to recognize that polar bears branched off of grizzly bears rather recently in evolutionary terms,” Kelly says, “and when a species splits into two it doesn’t happen overnight. It takes a period of isolation for them to evolve differences, and it often takes an even greater period of isolation for them to become so different that they can’t hybridize if they re-encounter one another.”
As the Arctic climate is fundamentally altered by rising temperatures and melting sea ice, grizzly and polar bears are sharing the same space more frequently than in the past. This has resulted in a new animal that in captivity, displays hunting behavior of the polar bear but without its superb swimming abilities. Marine mammals are also sharing new territory and there is evidence that they too are interbreeding. A skull of what seems to be a beluga-narwhal hybrid was discovered in Greenland and there have been sightings of a bowhead-right whale hybrid off the coast of Alaska.
While hybrid animals are fascinating, contemporary interbreeding may have devastating consequences for endangered animals like the polar bear. “People often think of extinctions as, well, simply, a population becomes smaller and smaller and smaller until there’s none left,” Kelly says. However, the reality is more complex. As the very specialized polar bear become increasingly likely to breed with the more generalized grizzly bear, the polar bear could eventually become consumed by this hybridization and effectively go extinct.
The disruptive influence of climate change may be simply too much for the polar bear to endure. “When environments change, that can lead to the proliferation of new species—what we call adaptive radiation,” Kelly says. “When environments change very abruptly, instead of leading to adaptive radiation it tends to result in large extinction events.”
Via Pacific Standard